The present invention relates to a compound for an electrolyte including a polymer compound and electrolyte salt. The invention also relates to an electrolyte, a process for producing the same and a battery using the same.
Recently, portable electrical products, such as a camcorder (video tape recorder), a cellular phone, and a laptop computer, are spreading quickly. Such electrical products require even higher performance of their electrochemical devices.
Conventional electrochemical devices such as a secondary battery utilize a liquid electrolyte obtained through dissolving electrolyte salt in, for example, water or flammable organic solvent as a substance to control ion conduction. However, since a liquid electrolyte has problems such as leaking, it is necessary to ensure liquid-tightness by using a metal container. Therefore, an electrochemical device generally becomes heavier and has the less versatility of possible form features. Furthermore, the sealing process is usually complicated. Research has been therefore made on so-called solid electrolytes, which consist of ion conductive solid. Solid electrolytes have no liquid leak. Solid electrolytes also have several other advantages, that is, simplified sealing process, lighter device, and the flexibility of the form selection due to the excellent ability of polymer to be molded into films.
Generally a solid electrolyte consists of a matrix polymer and electrolyte salt from which ion can be dissociated. The matrix polymer has ion dissociation power and has two functions: keeping this ion conductive solid in solid state and behaving as a solvent for electrolyte salt. Armand et al. at the Grenoble University (France) made a report on an example of the solid electrolytes in 1978; they achieved the ion conductivity of the order of 1xc3x9710xe2x88x927 S/cm in a system where lithium perchlorate was dissolved in polyethylene oxide. Since then, a variety of polymer materials are still examined actively, especially a polymer having a polyether linkage.
The solid electrolyte utilizes a normal chain polyether typified by polyethylene oxide as a matrix. This type of solid electrolyte achieves its ion conductivity by transferring the dissociated ions in the amorphous phase at the temperature above the glass transition point of the matrix polymer by the local segment movement of a polymer chain.
However, the ions, especially cations, dissociated into the normal chain matrix such as a polyethylene oxide, which is a semi-crystalline polymer, are strongly coordinated by the interaction with the polymer chain, and forms a pseudo-crosslinking point. This causes partial crystallization, which reduces the segment movement. In order to increase ion conductivity at room temperature, it is necessary to increase the ion dissociation power of the electrolyte salt and to develop a desirable molecular design for the polymer so that the polymer has many amorphous domains where the ions can move easily within a matrix, and the glass transition point of the polymer is kept lower.
In one molecular design, a branch structure is introduced into the polyethylene oxide frame in an attempt to increase ion conductivity (see Masayoshi Watanabe, Netsu Sokutei 24 (1) pp12-21, 1996). However, the synthesis of this type of polymer requires a complicated process.
In another molecular design, a three-dimensional network structure is introduced into a matrix polymer in an attempt to prevent the crystallization of polymer. This molecular design is applied to, for example, a polymer obtained by polymerizing acrylic or methacrylic monomers with polyoxyalkylene components (see Japanese Non-examined Patent Publication No. 5-25353). However, since alkali metal salt is not dissolved in a monomer very well, sufficient ion conductivity cannot be achieved. Therefore, it is necessary to obtain an alternative solid electrolyte.
The present invention has been made in view of such problems. An object of the present invention is to provide a compound for an electrolyte, and an electrolyte, a process for producing the same, and a battery using the same, capable of achieving high ion conductivity.
A compound for an electrolyte according to the present invention comprises a crosslinkable compound having an ether linkage and a functional group capable of forming a crosslink, a high-molecular compound, and electrolyte salt.
The compound for an electrolyte according to the present invention comprises a crosslinkable compound having an ether linkage and a functional group capable of forming a crosslink, a high-molecular compound, and electrolyte salt. This makes it possible to obtain an electrolyte which achieves high ion conductivity.
An electrolyte according to the present invention comprises a compound in which compounds having ether linkages and crosslinking groups are crosslinked by the crosslinking groups, a high-molecular compound, and electrolyte salt.
In the electrolyte according to the present invention, the high-molecular compound and the dissociated electrolyte salt are compatible with the compound in which compounds having ether linkages and crosslinking groups are crosslinked by the crosslinking groups. This enables the electrolyte to achieve high ion conductivity.
A process for producing an electrolyte according to the present invention involves: mixing crosslinkable compounds having ether linkages and functional groups capable of forming crosslinks, a high-molecular compound, and electrolyte salt; and crosslinking the crosslinkable compounds.
In the process for producing an electrolyte according to the present invention, crosslinkable compounds having ether linkages and functional groups capable of forming crosslinks, a high-molecular compound, and electrolyte salt are mixed, and the crosslinkable compounds are crosslinked.
Another process for producing an electrolyte according to the present invention involves: mixing crosslinkable compounds having ether linkages and functional groups capable of forming crosslinks, and a high-molecular compound; crosslinking the crosslinkable compounds; and adding electrolyte salt.
In the process for producing an electrolyte according to the present invention, crosslinkable compounds having ether linkages and functional groups capable of forming crosslinks, and a high-molecular compound are mixed, and the crosslinkable compounds are crosslinked. After that, electrolyte salt is added.
A battery according to the present invention comprises a positive electrode and a negative electrode, and an electrolyte, wherein the electrolyte comprises a compound in which compounds having ether linkages and crosslinking groups are crosslinked by the crosslinking groups, a high-molecular compound, and electrolyte salt.
The battery according to the present invention discharges as ions dissociated from the electrolyte salt move in the electrolyte between the negative electrode and the positive electrode. The battery, including the electrolyte according to the present invention, exhibits high ion conductivity and has high performance.
Other and further objects, features and advantages of the invention will appear more fully from the following description.